Power transmission belts, such as V-belts, are utilized in drive systems wherein the belt is trained about a plurality of pulleys. A common example of such a drive system is that of an automotive vehicle wherein the power transmission belt is trained about a drive shaft pulley and one or more pulleys for driving auxiliary equipment.
It has been found that in the operation of such a drive, the belt tends to change its length for a number of reasons. When the belt elongates, the tension in the belt drops so as to provide a reduction in the drive efficiency of the system.
It is, therefore, common to provide a belt tensioner in the form of an idler roller urged against the back side of the belt at a slack portion thereof between the drive pulley and the last driven pulley.
The idler roller is normally carried on the end of an idler arm which is swingably mounted to a support, such as a shaft mounted to the engine block, or the like. It is conventional to provide helical spring means for resiliently urging the arm to cause the idler roller to engage the belt and apply a tensioning force to the belt determined by the force of the spring means.
It is conventional to operate the spring means in torsion to bias the idler roller arm in the belt tensioning direction. Alternatively, it is known to utilize a cam unit and a spring operatively associated with the cam unit to effect the desired urging of the idler roller arm.
A problem has arisen in the use of such spring-biased tensioners, in that vibrations in the belt tend to cause the tensioner to vibrate causing variations in the belt tension, irregular wear of the belt, and possible movement of the belt from the drive system pulleys.
It is desirable to maintain an optimum tension in the belt at all times and such vibration prevents such maintained efficient operation of the drive system.